The nonlinear vibration analysis related to viscoelastic damper is investigated for the new whole-spacecraft passive vibration isolator. The stepped sinusoidal sweep test is performed and the results reveal the nonlinearity of the system. The nonlinear motion equation is developed. The frequency response equation is derived by the method of harmonic balance. The experiment of various excitation levels are carried out contrasting with numerical simulations. The nonlinear influence factors to the vibration isolation system are argued and the identification results explain the effect parameters on the performance of the vibration isolator. The research work is of significant implications for the analysis and design of passive vibration isolator for a wide range of practical applications.
This paper focuses on an active vibration isolator based on voice-coil motor (VCM). The isolator may reduce the vibration in the range from 5 to 100Hz in one DOF which can provide the payloads on a satellite a more stable working environment. A VCM is designed and optimized to provide enough feedback force; the state-space model is established according to the basic governing equations of the VCM. The LQR controller based on a reduced-order observer is designed for an output feedback control system. The vibration isolation system is verified by numerical simulations and experiments in which the VCM is installed between the payload and the excitation bottom, with an accelerometer located on the payload in the vertical direction. Both the simulation and experiment results show that the vibration of the payload is reduced effectively using the voice-coil actuator designed here.
The paper established the model of the practical Model test rig rotor-bearing system using finite element method, and discusses the phenomena of oil whirl and oil whip occurred in fluid lubricated bearing. The characteristics of stability of the nonlinear rotor-bearing system were numerically studied under different unbalance and different parameter of bearings, the model simulations are compared with measurements at the test rig, which can provide the theoretical reference for forecasting malfunction of oil film instability.
Cavitation typically occurs when the fluid pressure is lower than the vapor pressure at a local thermodynamic state. The aim of this paper is a numerical investigation of the cryogenic cavitation flow characteristics, considering variable thermodynamic properties of liquid nitrogen and numerical simulation liquid nitrogen around hydrofoil cryogenic cavitation flow characteristics. Based on homogeneous flow model and Zwart cavitation model, calculates hydrofoil isothermal and cryogenic cavitation in liquid nitrogen steadily, updates the evaporation and condensation coefficients of Zwart cavitation model, gives the hydrofoil surface pressure profile, temperature depression and distribution of cavitation intensity, contrasts the isothermal and cryogenic cavitation flow characteristics. Numerical results show that thermodynamics effect in cryogenic liquid cavitation significantly. Meanwhile, the hydrofoil surface pressure and temperature numerical results with experimental data and more Hord compared to verify the validity of the numerical simulation.
In this paper, the eigenvalue problem that involves uncertain-but-non-random parameters is discussed. The error of dynamical parameters of a system is unavoidable in the course of manufacture and installation. Eigenvalues of the system are hard to obtain by the traditional dynamical theory. A new method based on matrix inequality theory is developed to evaluate the upper and lower bounds of the eigenvalues. In this method, properties of matrix’s spectral radius and norm are used. The illustrative numerical examples are provided to demonstrate the validity of the method. Compared with the other methods, the calculated results show that the proposed method in this paper is effective in evaluating bounds of the eigenvalues of structures with uncertain-but-bounded parameters.
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